Why do you suppose many adults pine for the “good old days,” either an earlier era in history or their own youthful high school/college days? Is this generally a harmless or harmful thing? Why?

Maybe that was the peak of their existence. The time at which they'd accomplished most things, when they'd met the greatest people, when they'd fallen in love and fallen out.

It is harmless as long as they do not live in the past. Reminiscence is not a bad thing. But they have to remember to live in the present.

However, it's not the same for all adults.

Not everyone has had an eventful youth. For some, 'the time of their life' arrive at a later point. For others, it doesn't happen at all.

sorry no one is gonna answer you if you keep repeating the same question over and over again.

he uses the metaphor autumn.